The present invention relates to the field of photography and, more specifically, to an improved photographic film pack or assemblage of the type including a film container holding a supply of individual film units and a flat electrical battery for energizing electrical components of photographic apparatus configured to receive such an assemblage.
The commercially available SX-70 Land film pack or assemblage, manufactured by Polaroid Corporation, Cambridge, Mass., includes a generally box-like molded plastic film container defined by a forward wall having an exposure aperture therein; a rear wall oppositely spaced from the forward wall and having a pair of generally diamond-shaped battery terminal access openings therein; and a peripheral section joining the forward and rear walls and including a pair of side walls, a trailing end wall, and an oppositelyspaced leading end wall having a film withdrawal slot adjacent the forward wall.
When the container is molded, the leading end wall is formed in an open position, as a hinged extension of the rear wall, thereby leaving the leading end of the container open for insertion of the contents. After the contents are inserted through the open end by an automatic stuffing machine, the leading end wall is pivoted to its closed position and is bonded in place.
The contents of the film pack include, in stacked order from the interior surface of the forward wall to the interior surface of the rear wall, a dark slide for temporarily light-sealing the exposure aperture until the pack is loaded into the pack receiving chamber of a camera or camera back, a stack of integral self-developing film units (usually 10), a spring platen, and a substantially flat 6-volt battery having a pair of battery terminals on its underside which are located in facing registration with the access openings in the rear wall of the container.
The spring platen serves two functions. First, it urges the stack of film units upwardly toward the forward wall so that, following removal of the dark slide, the forwardmost film unit in the stack is always urged against the interior surface of the forward wall in position for exposure through the exposure aperture and subsequent advancement through the withdrawal slot by a camera pick mechanism for feeding the film unit into the bite of a pair of motor driven processing rollers. Secondly, the spring platen provides a downwardly directed biasing force on the battery for urging it toward the rear wall to maintain the battery terminals in good electrical contact with a pair of resiliently mounted battery contacts in the camera which extend through the access openings to engage the battery terminals.
For representative examples of such film packs, see commonly-assigned U.S. Pat. Nos. 3,543,662; 3,705,542; and 3,779,770, and copending application U.S. Ser. No. 026,200 filed on Apr. 2, 1979 (now U.S. Pat. No. 4,226,519).
The SX-70 Land film pack is intended for use with several types of battery energized photographic apparatus. These include several highly-automated self-developing cameras such as the SX-70, Pronto! and OneStep and a variety of motor-driven camera backs and special purpose industrial cameras, all manufactured by Polaroid Corporation.
Each such apparatus includes a receiving chamber into which the pack is slidably advanced to a fully inserted operative position and a pair of resiliently-displaceable battery contact members disposed on the bottom or rear wall of the chamber.
Typically, each battery contact member includes an upstanding, longitudinally extending, convexly-bowed leaf spring made of an electrically conductive material such as copper and an upwardly facing battery contact located at the apex portion of the leaf spring. The contact may be integrally formed with the leaf spring and comprise a coined or stamped area where the copper flares out laterally somewhat so that the contact area is wider than the leg portions of the leaf spring. In some commercially available cameras, this wider contact section is additionally coated with a highly-conductive material, for example silver, as disclosed in commonly-assigned U.S. Pat. No. 3,705,537.
As the film pack is inserted into the chamber, trailing end wall first, the trailing end portion of the container rear wall engages the upwardly sloping leaf spring sections, leading to the contacts, and compresses the springs downwardly so that the exterior surface of the rear wall rides over the contacts. As the container approaches the fully inserted position, the lateral distance between the edges of the diamond-shaped access openings becomes progressively larger and near the center of the access openings this distances exceeds the width of the contact thereby allowing the leaf springs to urge the contacts upwardly through the access openings into engagement with the battery terminals. As disclosed in the previously mentioned U.S. Pat. No. 3,705,537, the diamond-shaped access openings cooperate with the bowed leaf spring structure to smoothly cam the contacts into and out of the access openings to facilitate insertion/withdrawal of the film pack.
When the film container is fully loaded with 10 film units, the spring platen is in maximum compression and its spring force pushing downwardly on the battery substantially exceeds the spring force of the battery contact members pushing upwardly on the battery terminals so that the battery is firmly urged and retained against the interior surface of the container rear wall. This means that the depth of penetration of the contacts into the container through the access openings required to make good electrical contact with the battery is at a minimum. However, as the film units are sequentially exposed and withdrawn from the container, the spring platen expands accordingly and the downward force it exerts on the battery progressively decreases as each succeeding film unit is withdrawn. After 7 or 8 film units have been removed, the oppositely-directed spring forces of the spring platen and battery contact members are about in equilibrium. When the next film unit is withdrawn, the battery contact members provide the dominant force and they actually move at least that section of the battery having the terminals thereon upwardly slightly into the container to a new equilibrium position requiring a slightly greater depth of penetration by the battery contacts. Because the bow-shaped leaf springs are substantially longer than the diamond-shaped access openings, the ultimate depth of contact penetration has a limit because those portions of the arcuate leaf springs just forwardly and rearwardly of the contact will engage or "bottom out" on the edges of the access openings.
While the combination of this film pack and battery contact member configurations have proved to be highly reliable in maintaining good electrical contact with the battery while at the same time providing smooth and trouble free insertion/withdrawal of the film pack in millions of cameras and camera backs now in use, there are indications that a very small percentage of these cameras experience electrical failures in the middle of an automatic cycle of operation especially when there are only 2 of 3 film units left in the pack. It is suspected that most of these failures occur because of an interruption in electrical contact between one of the battery contacts and its corresponding battery terminal.
Tests have indicated that this failure can be reproduced when one of the leaf springs bottoms out while the other has sufficient clearance for a greater depth of penetration. In this case, the deeper penetrating battery contact will move the battery upwardly within the container to a point where there is a loss of contact between the battery contact and the facing battery terminal. Because the diamond-shaped opening is molded to great uniformity, it is most probable that this type of failure occurs when the profile shape of one battery contact member deviates (flattens out) substantially from the profile of its mate.
Such deviations in the profile shape of the arcuate battery contact members may be caused by a number of reasons. Because these cameras are manufactured in such high volumes, there will be some manufacturing variations in the tolerance of the leaf spring shape. More likely, however, is the fact that the copper leaf springs are fairly ductile and the configuration of one of these springs may be distorted or flattened out somewhat when the camera is in use in the field. One way this could happen is by the operator trying to jam an improperly oriented film pack into the receiving chamber or inadvertently inserting his fingers or other foreign object into the confines of the receiving chamber.
There have been numerous attempts to alleviate this problem. One proposed solution provides a stiffer spring platen within the container so that the battery is always positively urged against the interior surface of the rear wall against the bias of the battery contact members even when all of the film units have been removed from the container. While this solution minimizes the depth of contact penetration required for good electrical contact and allows a wider range of tolerances of the leaf spring profile configuration which can achieve such minimum penetration, the increased spring force by necessity is also transmitted to the stack of film units. The additional friction between the forwardmost film unit and the interior surface of the forward wall of the film container when the container is fully or almost fully loaded with film units results in a undesirable overloading of the camera pick mechanism which has overcome the increased friction to slide the film unit along the interior surface of the forward wall and through the film withdrawal slot subsequent to exposure.
Another proposed solution is to make the diamond-shaped access opening in the rear wall of the container longer to preclude premature bottoming out of a slightly deformed leaf spring. While this change will allow increase depth of contact penetration, thereby providing increased leaf spring shaped tolerances, the beneficial camming action for moving the contacts smoothly into and out of the access openings is compromised. More importantly, with longer diamond-shaped openings there is a tendency for the wider electrical contact to ride up into the container and become jammed into the narrowing V-section of the trailing end of the access openings thereby preventing withdrawal of the film pack from the chamber.
Therefore, it is an object of the invention to provide an improved photographic film assemblage of the type described having provision for increasing the reliability of maintaining good electrical contact between the terminals of a flat battery in the film container and the battery contact members in photographic apparatus configured to receive such an assemblage.
It is another object to provide such an assemblage wherein the cost of the improvement is low and requires minimal modification to one component of the assemblage and existing manufacturing and assembly equipment.
Another object is to provide such an assemblage which will be more reliable when used with photographic apparatus having one or more battery contact members that may deviate from its original manufactured configuration due to inadvertent distortion.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.